Cooking of drying oils and varnishes



My 18, 1939. H. v. A. m5:- 1 2,166 539 COOKING OF DRYING OILS AND VARNISHES I Filed May 5, 1937 INVENTOR Hmry 1 2mm! liz'rd Bnlscae I, 244 m rznsvs M Patented July 18, 1939 UNITED STATES COOKING F DRYING OILS AND VAR-NISHES Henry Vincent Aird Briscoe, Barnes, London, England Application May 5, 1937, Serial No. 140,832 In Great Britain May 8, 1936 3 Claims.

This invention is concerned with the cooking of drying oils and varnishes for the purpose of thickening such materials by prolonged heating with consequent polymerisation of the oils and/or resinous products dissolved therein. In the case of varnishes the cooking process maybe preceded by the usual running or melting of the gum or resin and the addition of hot drying oil thereto in order to produce the crude varnish or by other like preliminary operations.

It has been found that during the process of cooking or polymerisation there are produced in the varnish or oil certain by-products such as free fatty or resinous acids and certain hydrocarbons which, if left in the oil or varnish, have a deleterious effect upon its properties. These deleterious by-products are more volatile than the oil or varnish in which they occur and may therefore be removed to a considerable extent by evaporation or distillation under suitable conditions.

V The present invention is concerned with an improved process whereby the removal of deleterious volatiles can be effected during the process of cooking oil or varnishes in large closed kettles under an inert atmosphere according to the well-known procedure.

According to the invention the process for treating drying oils or varnishes during their cooking or polymerisation in closed kettles is characterised by the steps of withdrawing a proportion of the hot oil or varnish continuously or intermittently at frequent intervals from the kettle during a major part of the said process of cooking or polymerisation, subjecting the oil or varnish thus withdrawn while still at or near the kettle temperatures to a distilling operation under vacuum in a separate distillation chamber and returning it whilestill hot continuously or intermittently to the kettle against atmospheric pressure, the said steps being effected in such a way that the whole of the oil or varnish is subjected repeatedly to the said distilling operation while the cooking or: polymerisation is being carried out.

According to anembodiment of the invention the process for treating drying oils or varnishes during their cooking or polymerisation in closed kettles consists in continuously withdrawing a fraction of the oil or varnish from the kettle, subjecting the fraction in a separate smaller chamber in thin layers or in a disperse condition to a high vacuum to remove the undesired volatile matters which are distilled oil and condensed and collected apart and then returning the residue of the fraction to the kettle against atmospheric pressure by means of an oil pump or injector by collecting it alternately in evacuated receivers each of which when full can be shut ofi from the distillation chamber and opened to 5 atomspheric pressure so that the hot oil may be drained back to the kettle by gravity.

The distillation chamber and the pipe systems for circulating the oil or varnish therethrough' are preferably so constructed that the chamber can readily be opened for cleaning and again closed vacuum-tight. When distributing plates are fitted to the distillation chamber these are preferably made detachable so that when the chamber is opened they can easily be removed for cleaning and replaced. The distillation chamber and the circulating pipes, pump, etc., connected therewith are preferably heat-insulated so that the temperature of the oil or varnish in circulation is maintained substantially at the working temperature.

The cooking of the oil or varnish may be carried out in any of the known types of large closed kettles, often holding as much as two tons or more of material, and provided with stirring gear, froth breaking devices, a fume exhaust and condenser and means for introducing and maintaining an atmosphere of inert gas such as carbon dioxide above the liquid. Kettles for the cooking of stand-oil may be worked quite full and provided with overflow pipes leading to a reservoir in known manner. I

It is a known process to take a fully cooked oil or varnish and subject it to vacuum distillation in suitable apparatus. From this the present process difiers in continuously and repeatedly subjecting the oil or varnish to vacuum distillation throughout the whole or the larger part of the process of cooking. This has the advantage of reducing substantially the time required for cooking to a given viscosity; for example under conditions where the volatiles are removed continuously from a varnish as they are formed a given viscosity required for an ordinary shortoil copal varnish may be attained in one-t0 two hours less than the normal cooking period of, say

five to seven hours.

It is also known to apply vacuum to the cooking kettle so as to favour the removal of fume and volatiles but this procedure has three imor break-down in such a system is fraught with grave danger of fire and explosion which must involve the whole contents of the kettle; thirdly, as such large kettles for oil or varnish are usually constructed of aluminium which suffers a considerable loss of strength at the working temperature of about 280 to 300 C. there is a grave risk of collapse of the kettle, were it to be subjected to an external pressure of 15 lbs./sq. in. by evacuating the interior. It is for these reasons practically advantageous to conduct the vacuum distillation in a relatively small and strong separate chamber to which the contents of the kettle can be fed by the atmospheric pressure existing in the kettle through a valve or like controlling means and from which the residual oil or varnish may be returned by a suitable pump or other means according to this invention.

In carrying the invention into efiect there is attached to a large closed kettle of any known type, heated in any known manner, additional distillation apparatus of the kind hereinafter described. A pipe, preferably so constructed as to facilitate cleaning Withdraws hot oil or varnish from a point below the usual working level of the liquid in the kettle and the flow of the liquid is controlled by a valve or valves and/or by a suitable orifice plate or several such plates in series. Between this control means and the distillation chamber the liquid may and preferably should pass a sight glass so that the flow may be observed and controlled. The hot liquid then enters a distillation chamber which is pref erably small relative to the kettle and is there distributed by any convenient means, e. g., by being spread over inclined shelves or by being distributed over packing material such as Raschig Rings contained therein, so as to present a large surface. Alternatively the liquid may be broken up by a suitable jet into stream or droplets which are allowed to fall freely through the distillation chamber.

In any case this chamber is subjected to vacuum by being connected by one or more short wide pipes or channels to a tubular or other condenser which is cooled, e. g., by water, and connected with a dry vacuum pump. The condensate collecting in the condenser is received in a suitable receiver which is connected also to the vacuum line and provided with suitable cocks whereby it can be cut oil from both condenser and vacuum pump and emptied by opening the lower cock and admitting air above the liquid. Alternatively this receiver may be provided with a small pump of suitable type whereby the condensate is extracted against atmospheric pressure.

The residual oil or varnish is accumulated in one of two alternative receivers from which it can be drained back to the kettle in the manner already described or alternatively after distillation and continuously as it is distilled is taken from the bottom of the distillation chamthe distillation vessel. The rate of circulation should be such that the whole body of oil goes through the distillation vessel several times during the process of cooking and preferably several times per hour.

An embodiment of this invention is illustrated in the accompanying drawing applied to a twoton aluminium stand-oil kettle A, fitted with a stirrer B, a froth breaker C, and an overflow pipe D leading to a reservoir E which is vented to the atmosphere at F, the kettle being seated in a brick setting G and heated by the oil burner H. The kettle is provided with a small inlet pipe for carbon dioxide J and with a pipe K leading to the pump L whereby the contents of the kettle can be discharged or, if desired, circulated through a cooling tank or other cooling system and returned through pipe and cock M. All this is in accordance with well known practice.

, Tothis plant, according to the present invention is added the system whereby atmospheric pressure in A forces hot oil up the pipe N and, M being closed and open, a stream of hot oil, regulated by the control valve P, is fed through the inlet pipe Q into the vacuum distillation chamber R where it flows down in a thin film over the conical distributor S and then by way of the drain pipe T to the hot oil pump U and is thereby pumped back into the kettle against atmospheric pressure through the pipe K. Vapours liberated from the oil in R pass by the wide pipe V to a water-cooled tubular condenser W and there condense and collect in a receiver X which can be drained from time to time. The distillation continues uninterruptedly, by shutting the cooks I and 2 and opening the cocks 3 and 4. In reconnecting the receiver X to the condenser, cocks l, 3 and 4 are shut, and then cock 5 is shut while 2 is opened until the vacuum pump Y has produced a sufficiently high vacuum in X. Then cocks I and 5 are opened and collection of distillation in X proceeds as before. The vapour pipe V is provided with an internal gutter Z or equivalent device to trap reflux which is drained into the receiver. The setting of the control valve P and the size and speed of the pump U are such that the whole contents of the kettle are circulated through R about twice or-three times per hour and this rate of distillation is maintained during "the greater part of the cooking process and up to the end' of that process. The distillation is conducted under a pressure of 1 to mm. merthat undesired volatiles can be efliciently and safely removed from hot oil and varnish continuously as cooking proceeds thereby yielding improved products in relatively shorter cooking time What I claim is:

1*. A process for treating drying oils or varnishes during their cooking or polymerisation, comprising the steps of heating the oil or varnish in a. closed kettle at substantially atmospheric pressure to cook or polymerise the same, withdrawing a proportion of the hot oil or varnish from the said kettle during a major part of the said process of cooking or polymerisation and introducing it into a separate distillation chamber, subjecting the oil or varnish thus withdrawn while still ator near the kettle temperature to a distilling operation under vacuum in 'said separate distillation chamber and returning it while still hot to'the kettle against the pressure in said kettle, repeating said steps with different portions of said oil or varnish so that the whole body of the-oil or varnish is subjected repeatedly to the said distilling operation while the cooking or polymerisation is being carried out.

2. A process for treating drying oils or var- 'nishes during their cooking or polymerisation, comprising the steps of heating the oil or varnish in a closed kettle at substantially atmospheric pressure to cook or polymerise the same, withdrawing a proportion of the hot oil or varnish continuously from the said kettle during a major part of the said process of cooking or polymerisation and introducing it into a separate distillation chamber, subjecting the oil or varnish thus withdrawn while still at or near the kettle temperature to a distilling operation under vacuum r in said separate distillation chamber and returning it while still hot continuously to the kettle against the pressure in said kettle, repeating said steps with different portions of said oil or varnish so that the whole body of the oil or varnish is subjected repeatedly to the said distilling operation while the cooking or polymerisation is being carried out.

3 A process for treating drying oils or var= nishes during their cooking or polymerisation, comprising the steps of heating the oil or varnish in a closed kettle at substantially atmospheric pressure to cook or polymerise the same, withdrawing a proportion of the hot oil or varnish intermittently at frequent intervals from the said kettle during a major part of the said process of cooking or polymerisation and introducing it into a separate distillation chamber, subjecting the oil or varnish thus withdrawn while still at or near the kettle temperature to a distilling operation under vacuum in said separate distillation chamber and returning it intermittently to the kettle against the pressure in said kettle, repeating said steps with difierent portions of said all or varnish so that the whole body of the oil or varnish is subjected repeatedly to the said distilling operation while the cooking or polymerisation is being carried out.

HENRY VINCENT AIRD BRISCOE. 

